1. Field of the Invention
The present invention relates to an optical system driving device, and to an optical recording apparatus incorporating this device.
2. Related Arts
Optical recording mediums, such as magneto-optical disks (MO) or CD-ROMs, which are employed in accordance with various specifications, are in wide use today. And for the optical recording apparatuses that are used to record and reproduce data on such optical recording mediums, optical systems which can project laser beams onto recording faces, or which can receive light reflected from the recording faces, are indispensable.
Further, since to access a predetermined recording track on a recording face a laser beam must be focused on that track, an optical system driving device is also required.
FIG. 7 is a top view of a partial arrangement for an optical recording apparatus, including an optical system driving device which is used for recording and for reproduction. In FIG. 7, an optical recording medium is mounted, with its recording face down, on a shaft which is rotated by a spindle motor 101, and a lens actuator (an optical system driving device) 20 is positioned opposite the recording face of the optical recording medium.
The optical system driving device 20 is driven in the radial direction of the optical recording medium along rails 13 and 14. An object lens 1, which is an optical element, is controlled so that it faces in the direction perpendicular to the recording face of the optical recording medium (the focusing direction), thereby enabling the continuous focusing of a laser beam on a recording track.
FIG. 8 is a partially enlarged perspective view of the optical system driving device 20. The two rails 13 and 14 pass through a carriage 11, on opposite sides of which are provided carriage coils 15 and 16.
When the carriage coils 15 and 16 are electrified, a driving force is generated between magnetic circuits (not shown), and the carriage 11 is displaced along the rails 13 and 14 in the tracking directions indicated by a double-headed arrow in FIG. 8.
A holder 2, which supports the object lens 1, and a support section to which the holder 2 is connected are mounted so that they are recessed in a hollow portion of the carriage 11. Provided as a part of the support section is an elastic member 3, and coils (hidden in FIG. 8) provided on opposite sides of the holder 2 face magnetic circuits 9 and 10.
FIG. 9 is a schematic cross-sectional view of the center portion of the optical system driving device 20 viewed from the direction indicated by an arrow in FIG. 7. In FIG. 9, the optical path of a laser beam 110 is changed perpendicularly by a reflection mirror 12. When a coil 7 (a coil 8 is located on the opposite side) is electrified, a driving force is generated between the magnetic circuits 9 and 10 in FIG. 8, and the holder 2 is displaced. Therefore, the object lens 1 is controlled perpendicular to the recording face of the optical recording medium, and the laser beam 110 is focused on a recording track.
The above described arrangement is the general arrangement of the optical system driving device of the optical recording apparatus. For this arrangement, it is particularly important that the focus of the laser beam 110 be precisely positioned on the recording face of the optical recording medium. Thus, the holder 2 is supported by the support section, and is displaced by the driving force generated between the magnetic circuits 9 and 10 by the current which is supplied to the coils 7 and 8, as was previously described. The problem encountered here results from the unwanted vibration of the elastic member 3, which constitutes part of the support section.
In order to prevent unwanted vibration, conventionally, as is shown in FIGS. 10A to 10C, a vibration damping sheet 30 is attached to a leaf spring 3. In addition, a power supply path 41, which is formed on a flexible printed board 40, supplies a current to the coil 7, and the resultant board 40 is stacked with the vibration damping sheet 30, as is shown in FIG. 10C.
As part of the manufacturing process, the attachment of the vibration damping sheet to the leaf spring 3 complicates the assembly of the optical system driving device 20, and the associated structural requirements increase the number of parts that must be used. In addition, since the flexible printed board 40 is laminated with the vibration damping sheet 30, the rigidity of the leaf spring 3 is increased.
Therefore, the primary resonance frequency in the direction in which the holder 2 is displaced, i.e., in the focusing direction, is increased, and focusing control is difficult.
As another technique, disclosed in Japanese Unexamined Laid Open Patent Publication No. Sho 61-258346 is similar to the arrangement shown in FIGS. 2 and 3 wherein a viscous member is located near the fixed end of a leaf spring and is held by the leaf spring. Further, according to an apparatus disclosed in Japanese Unexamined Laid Open Patent Publication No. Hei 5-325319, a holder on which an object lens is mounted is supported by a leaf spring, and the end of the leaf spring is connected to a fixed member via a sticky member.
As is described above, in a conventional device, the sticky member is provided to reduce the unwanted vibration of the leaf spring. However, a specific structure has not been proposed which would provide for such a sticky member to be introduced and located in the vicinity of the end of the leaf spring.
In Japanese Unexamined Laid Open Patent Publication No. Hei 9-54960, it is taught that a damper member is introduced through a positioning hole which is formed in a leaf spring. However, formation of a hole in a leaf spring to introduce a damper results in a decrease of rigidity of the leaf spring, and if a thicker leaf spring is prepared and used, the primary resonance frequency required for focusing will be increased.
As the carriage 11 (see FIG. 8) is moved in the radial direction of the optical recording medium, inertial forces which act on the lens holder 2 are generated at an elastic focus spring, i.e., the leaf spring 3. Thus, resonance of the leaf spring 3 occurs in the axial direction (direction in which the leaf spring 3 is extended and contracted).
The occurrence of resonance in the axial direction (hereinafter referred to as an axial resonance frequency) can not be avoided. It is preferable that the resonance frequency be increased so that it is as high as possible and so that the ratio of this frequency to the previously described primary resonance frequency be increased.
One objective of the present invention, therefore, is the provision of an optical system driving device for preventing the unwanted vibration of an elastic member supporting a holder on which an object lens is mounted, as well as resolving a resonance frequency problem, and the provision of an optical recording apparatus incorporating such an optical system driving device.
Another objective of the present invention is the provision of an optical system driving device for resolving a resonance frequency problem affecting an elastic member supporting a holder on which an object lens is mounted, as well as increasing manufacturing efficiency and reducing the number of parts required, and the provision of an optical recording apparatus incorporating such an optical system driving device.
To achieve the above objectives, according to the present invention, basically, an optical system driving device includes:
a holder, which holds an optical element;
support means for supporting the holder and permitting its displacement in a focusing direction;
a carriage, in which both the holder and the support means are mounted and which moves in a tracking direction; and
drive coils, which are included in the holder for displacing the holder in the focusing direction; and
a flexible printed board for supplying a drive current to the drive coils.
The support means includes a fixed portion and an elastic member, one end of which is fixed to the fixed portion and the other end of which is connected to the holder. Further, a vibration damping member, connected to the fixed portion, is mounted on the side of the elastic member and is sandwiched between the flexible printed board and the elastic member.
As the first feature of the arrangement, the vibration damping member is sticky, and one face adheres to the flexible print substrate.
As the second feature of the arrangement, the vibration damping member is one quarter to one third as long as the elastic member.
As the third feature of the arrangement, the elastic member has a pair of parallel leaf springs.
Further, to achieve the above objectives, according to a different arrangement an optical system driving device includes:
a holder, which holds an optical element;
support means, for supporting the holder and permitting the displacement of the holder in a focusing direction;
a carriage, in which the holder and the support means are mounted and which moves in a tracking direction; and
drive coils, which are included in the holder and which cause the holder to be displaced in the focusing direction; and
a flexible printed board, for supplying a drive current to the drive coils,
wherein the support means includes a fixed portion and a pair of leaf springs, each of which is secured at one end to the fixed portion and is connected at the other end to the holder, and
wherein a rectangular hole is formed in the free length portion of each of the leaf springs, so that one side of each of the rectangular holes is substantially aligned with an end side of the fixed portion.
As the first feature of the different arrangement, a pair of parallel leaf springs is used, one end of each is secured, one to the upper and one to the lower face, of the fixed portion.
As the second feature of the different arrangement, the hole is a rectangle, the long sides of which parallel the direction corresponding to the width of the leaf spring.
As the third feature of the different arrangement, the fixed portion has on one side, facing the holder, a first upright portion, and on the opposite side, paralleling the first upright portion, a second upright portion. The sides of the fixed portion are substantially aligned with sides of the rectangular holes formed in the free length portions of the leaf springs.
As the fourth feature of the different arrangement, grooves are formed between the first and the second upright sections of the fixed portion, and the rectangular holes, which are formed in the leaf springs, have long sides which are parallel to the widthwise direction of the fixed portion and short sides which are shorter than the width of the grooves between the first and the second upright sections.
As the fifth feature of the different arrangement, grooves are formed between the first and the second upright sections of the fixed portion, and a vibration damping material is fed through the rectangular holes until it fills the grooves.
Further, to resolve the conventional problem, an optical recording apparatus comprises:
a drive mechanism for rotating a recording medium; and
the optical system driving device, which has one of the above described features, wherein the optical element is located opposite the recording face of the recording medium.